1. The Field of the Invention
This invention relates generally to antennas, filters and transmission lines. More specifically, the invention relates to a new configuration of a continuous transverse stub element array structure which is formed in a coaxial arrangement to provide superior omnidirectional performance at microwave, millimeter, and quasi-optical wavelengths.
2. The State of the Art
The state of the art of antennas, antenna arrays, parallel plate waveguides, filters and couplers beginning at microwave frequencies is characterized, for example, by several types of more conventional designs of mono-poles or dipoles, slotted waveguide arrays, printed patch arrays, and reflector and lens systems as mobile or base station terminal antennas. These designs are used to build high gain antenna arrays, adaptive arrays, phased arrays and smart antennas. Furthermore, when moving into frequencies which are greater than 20 GHz and commonly known as millimeter wave and quasi-optical frequencies, antennas and filters suffer from relatively low Q factors due to high dissipative conductor and dielectric losses, interconnect losses, and from relatively difficult fabrication due to dimensional tolerances. Accordingly, antenna and filter designs have moved to more advantageous configurations which are known as continuous transverse stub element array structures which can be radiating (antenna) or reactive (filter).
The known configurations and methods of fabricating these continuous transverse stub element array structures are generally taught, for example, in U.S. Pat. Nos. 5,266,961, 5,412,394, 5,583,524, 5,604,505 and 5,771,567 to list but a few. In essence, these patents teach that a continuous transverse stub element residing in one or both conductive plates of a parallel plate waveguide is employed as a coupling, reactive, or radiating element in coupler, filter and antenna designs. These patents contributed to the parallel-plate continuous transverse array designs that are characterized by pencil beam patterns.
In the planar-type prior art, a typical continuous transverse stub element array structure will include a dielectric element forming a plane which has a second dielectric element which extends transversely to the plane to form a stub. A first conductive element is disposed coextensive with the dielectric element forming the plane, and a second conductive element is disposed along a surface of the second dielectric stub element.
FIG. 1 is provided as a close-up illustration of the prior art which shows a typical dielectric plane 10 and stub element 12. FIG. 2 is provided to show a perspective view of an array of stub elements 14 in a planar array 16.
It is taught in the prior art that purely-reactive stub elements are realized through conductively terminating (a short circuit) or by narrowing (an open circuit) the terminus of the stub element. Radiating elements are formed when stub elements of moderate height are opened to free space. Precise control of stub element coupling or excitation by way of coupling of parallel plate waveguide modes is accomplished through variation of longitudinal stub element length, stub element height, parallel plate separation, and the properties of the parallel plate and the stub element media.
The prior art is also characterized by teaching that continuous transverse stub elements can be arrayed to form planar apertures and structures of arbitrary area which are comprised of a linear array of continuous transverse stub elements fed by a conventional line-source or sources.
The prior art teaches that the transverse stub elements are varied by modifying their height, width, length, and cross section. Other cited variations include changing the number of stub elements, and adding additional structures to the basic stub element. However, these arrays structure fail to provide a coaxial arrangement for a filter or antenna array system, or any means of conveniently providing a signal feed thereto.
It would be an advantage over the prior art to provide a different continuous transverse stub element array design which can provide a high Q-factor filter and a low cost antenna array with two-dimensional beam steering capability. It would be another advantage to provide omnidirectional capabilities at microwave, millimeter wave and quasi-optical wavelengths which would permit construction of a small and mobile array design. It would be a further advantage to provide a large beam scan width in a new continuous transverse stub element array design which provided low loss and had improved impedance matching.